1. Field of the Invention
Aspects of the present invention relate to a positive electrode for a rechargeable lithium battery, and a rechargeable lithium battery including the same. More particularly, aspects of the present invention relate to a positive electrode for a rechargeable lithium battery that suppresses side-reactions between the positive electrode and an electrolyte.
2. Description of the Related Art
Lithium rechargeable batteries have recently become popular as power sources for small portable electronic devices. These batteries use an organic electrolyte solution, and thereby have twice the discharge voltage of a conventional battery using an alkaline aqueous solution, and accordingly, have a higher energy density.
Research into positive active materials for a rechargeable lithium battery has been conducted on lithium-transition element composite oxides that are capable of intercalating lithium, such as, LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, and the like.
As for a negative active material for a rechargeable lithium battery, various carbon-based materials such as artificial graphite, natural graphite, and hard carbon have been used, which can all intercalate and de-intercalate lithium ions. A graphite negative active material increases the discharge voltage and energy density of a battery because it has a low discharge potential of −0.2V, as compared to lithium. A battery using graphite as a negative active material has a high average discharge potential of 3.6V, and an excellent energy density. Furthermore, graphite is the most comprehensively used material, among the aforementioned carbon-based materials, because graphite guarantees a better cycle life for a battery, due to its outstanding reversibility. However, a graphite negative active material has a low density, and consequently a low capacity in terms of energy density per unit volume. Further, graphite has problems relating to explosion or combustion when a battery is misused or overcharged, and the like, because graphite is likely to react with an organic electrolyte at a high discharge voltage.
In order to solve these problems, a great deal of research on oxide negative electrodes has recently been performed. For example, amorphous tin oxide, developed by Japan Fuji Film Co., Ltd., has a high capacity per weight (800 mAh/g). However, this oxide has resulted in some critical defects, such as, a high initial irreversible capacity of up to 50%. Furthermore, some of the tin oxide has tended to be reduced into tin metal during the charging or discharging reaction, which limits its acceptance for use in a battery.
An example of another oxide negative electrode is the negative active material LiaMgbVOc(0.05≦a≦3, 0.12≦b≦2, 2≦2c−a−2b≦5), that is disclosed in Japanese Patent Publication No. 2002-216753.
However, such an oxide negative electrode does not show a sufficient battery performance, and therefore, a great deal of research into oxide negative materials has been conducted.